The military's watchdog has found hundreds of flaws in the way giant defense contractors produced the F-35 fighter jet – flaws that made what was already the most expensive weapons system in history even more costly to American taxpayers and flaws that should have been caught by the program's military overseers.

The Department of Defense Inspector General released a 126-page report today describing 719 "issues" it found with the jet's primary manufacturer, Lockheed Martin, and five other major contractors as they assembled planes for the estimated nearly $400 billion F-35 Joint Strike Fighter program. It also listed failures of the F-35 Joint Program Office (JPO), the military-led organization in charge of putting the planes in the air for three services in the American military, for not ensuring "Lockheed Martin and its subcontractors were applying rigor to design, manufacturing, and quality assurance" among other things. Both Lockheed Martin and the JPO said the report was old news and that the issues have been mostly addressed.

Flaws found on the production line, according to the DOD IG, included "uncontrolled or unapproved" design changes in production planning, contractor personnel who were not following written manufacturing and assembly process instructions, inadequate calibration management systems that could hinder testing and employees with expired certifications for critical tasks like ejection seat installation or "explosives care."

Taken together, the DOD IG said the flaws "could adversely affect aircraft performance, reliability, maintainability, and ultimately program cost."

The strategy for producing the F-35, which included beginning manufacturing before the first test flight even took off, has been widely criticized – called "acquisition malpractice" by the Pentagon's top weapons buyer in 2012.

In response to the DOD IG report, the F-35 JPO released a statement noting that of the 363 finding – under which the DOD IG described the 719 "issues" – 343 corrective action recommendations (CARs) were activated and 269 of them have already been closed "with the remaining 74 still in work."

"The report is thorough, professional, well documented and useful," the JPO statement said. "A majority of the findings are consistent with weaknesses previously identified by the Defense Contract Management Agency (DCMA) and the F-35 Joint Program Office (JPO), and do not present new or critical issues that affect the health of the program."

Lockheed Martin issued a statement as well that said the DOD IG's report is "based on data that's more than 16 months old and [a] majority of the Corrective Action Requests identified have been closed." The DOD IG report said it conducted its audit during fiscal years 2012 and 2013.

"Producing quality products is a top priority for the F-35 Program, and Lockheed Martin and its suppliers strive every day to deliver the best aircraft possible to our customers," the Lockheed statement said. "When discoveries occur, we take decisive and thorough action to correct the situation. Our commitment is to deliver the F-35's world class Fifth Generation fighter capabilities to the warfighter on time and within budget."

In the statement, Lockheed Martin is presumably referring to the military's latest, revised cost and timeline estimates – which include a combat-ready variant by 2015 – as in the past the program has repeatedly suffered significant cost overruns and delays. Back in 2001, the military believed the fighter would be ready by 2012. As of June this year, however, the Government Accountability Office estimated that only about a third of necessary developmental testing had been completed on the complex plane.

Military defenders of the plane have said that the stealth F-35, when ready, will serve as the backbone of American air dominance for decades to come, with unprecedented fighting, flying and electronic warfare capabilities, flying in concert with the air-to-air dogfighting F-22 Raptor.

"The air superiority this nation has enjoyed for 60 years is not an accident and gaining and maintaining it is not easy," Air Force Gen. Mark Welsh III said during testimony at a Senate Armed Services subcommittee hearing in June. "I believe the F-35 is essential to ensuring we can provide that air superiority in the future."

High-profile detractors, like Sen. John McCain, R-Ariz., have called it "worse than a disgrace."

"It's still one of the great national scandals that we have ever had as far as the expenditure for taxpayers' dollars are concerned," said McCain during another Senate Armed Services Committee Hearing earlier this month, as reported by DOD Buzz.